Radio astrometry with chromatic AGN core positions

Porcas, R. W.

doi:10.1051/0004-6361/200912846

Cited by 66 publications

(70 citation statements)

References 19 publications

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“…This is expected as the radio emission in B1422+231 is slightly extended and is likely not to originate in the accretion disk (as observed in the optical range) but rather from a nearby region at the basis of the radio jet. This effect, known as core-shift, is observed between two different radio-bands (Porcas 2009;Kovalev et al 2008) and may induce astrometric perturbations as large as a few mas on the relative astrometry of lensed quasar images (Mittal et al 2006). Thus, it appears that the use of radio data as an independant calibrator of the systematic errors is difficult at such an accuracy.…”

Section: Resultsmentioning

confidence: 99%

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

Chantry¹,

Sluse²,

Magain³

2010

A&A

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Aims. We attempt to place very accurate positional constraints on seven gravitationally lensed quasars currently being monitored by the COSMOGRAIL collaboration, and shape parameters for the light distribution of the lensing galaxy. We attempt to determine simple mass models that reproduce the observed configuration and predict time delays. We finally test, for the quads, whether there is evidence of astrometric perturbations produced by substructures in the lensing galaxy, which may preclude a good fit with the simple models. Methods. We apply the iterative MCS deconvolution method to near-IR HST archival data of seven gravitationally lensed quasars. This deconvolution method allows us to differentiate the contributions of the point sources from those of extended structures such as Einstein rings. This method leads to an accuracy of 1-2 mas in the relative positions of the sources and lens. The limiting factor of the method is the uncertainty in the instrumental geometric distortions. We then compute mass models of the lensing galaxy using state-of-the-art modeling techniques. Results. We determine the relative positions of the lensed images and lens shape parameters of seven lensed quasars: HE 0047-1756, RX J1131-1231, SDSS J1138+0314, SDSS J1155+6346, SDSS J1226-0006, WFI J2026-4536, and HS 2209+1914. The lensed image positions are derived with 1-2 mas accuracy. Isothermal and de Vaucouleurs mass models are calculated for the whole sample. The effect of the lens environment on the lens mass models is taken into account with a shear term. Doubly imaged quasars are equally well fitted by each of these models. A large amount of shear is necessary to reproduce SDSS J1155+6346 and SDSS J1226-006. In the latter case, we identify a nearby galaxy as the dominant source of shear. The quadruply imaged quasar SDSS J1138+0314 is reproduced well by simple lens models, which is not the case for the two other quads, RX J1131-1231 and WFI J2026-4536. This might be the signature of astrometric perturbations caused by massive substructures in the galaxy, which are unaccounted for by the models. Other possible explanations are also presented.

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Section: Resultsmentioning

confidence: 99%

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

Chantry¹,

Sluse²,

Magain³

2010

A&A

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“…Such offsets are expected for several reasons: i) the observations were conducted at different frequencies; ii) the different campaigns used different calibrator sources, which may have different systematic errors (e.g. Kovalev et al 2008;Porcas 2009;Sokolovsky et al 2011) in their ties to the International Celestial Reference Frame (ICRF2, Ma et al 2009); iii) the data were obtained at times that are up to ten years apart during which improvements to the correlator models and Earth orientation parameters introduce offsets; and iv) the data were taken with different instruments (VLBA and EVN) that use different hardware/software correlators. Table 5 summarizes the estimates of µ and π from the individual fits, from the different combinations of data sets, and from the bootstrapping method (where we quote the most compact 68% confidence interval), as well as the implied pulsar distances and transverse velocities.…”

Section: Estimates For Astrometric Parameters Of B1929+10 B2020+28 mentioning

confidence: 99%

Revisiting the birth locations of pulsars B1929+10, B2020+28, and B2021+51

Kirsten

Vlemmings

Campbell

et al. 2015

A&A

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We present new proper motion and parallax measurements obtained with the European VLBI Network (EVN) at 5 GHz for the three isolated pulsars B1929+10, B2020+28, and B2021+51. For B1929+10 we combined our data with earlier VLBI measurements and confirm the robustness of the astrometric parameters of this pulsar. For pulsars B2020+28 and B2021+51 our observations indicate that both stars are almost a factor of two closer to the solar system than previously thought, placing them at a distance of 1.39 +0.05 −0.06 and 1.25 +0.14 −0.17 kpc. Using our new astrometry, we simulated the orbits of all three pulsars in the Galactic potential with the aim to confirm or reject previously proposed birth locations. Our observations ultimately rule out a claimed binary origin of B1929+10 and the runaway star ζ Ophiuchi in Upper Scorpius. A putative common binary origin of B2020+28 and B2021+51 in the Cygnus Superbubble is also very unlikely.

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“…Popović et al 2012;Porcas 2009;Taris et al 2011). Linear trends of these shifts might lead to spurious proper motions measured for quasars and stable over years to decades.…”

Section: Spurious Proper Motion From Variable Source Structurementioning

confidence: 99%

Quasars can be used to verify the parallax zero-point of theTycho-GaiaAstrometric Solution

Michalik

Lindegren

2016

A&A

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Context. The Gaia project will determine positions, proper motions, and parallaxes for more than one billion stars in our Galaxy. It is known that Gaia's two telescopes are affected by a small but significant variation of the basic angle between them. Unless this variation is taken into account during data processing, e.g. using on-board metrology, it causes systematic errors in the astrometric parameters, in particular a shift in the parallax zero-point. Previously, we suggested an early reduction of Gaia data for the subset of Tycho-2 stars (Tycho-Gaia Astrometric Solution; TGAS). Aims. We investigate whether quasars can be used to independently verify the parallax zero-point in early data reductions. This is not trivially possible as the observation interval is too short to disentangle parallax and proper motion for the quasar subset. Methods. We repeat TGAS simulations but additionally include simulated Gaia observations of quasars from ground-based surveys. All observations are simulated with basic angle variations. To obtain a full astrometric solution for the quasars in TGAS we explore the use of prior information for their proper motions. Results. It is possible to determine the parallax zero-point for the quasars with a few µas uncertainty, and it agrees to a similar precision with the zero-point for the Tycho-2 stars. The proposed strategy is robust even for quasars exhibiting significant spurious proper motion due to a variable source structure, or when the quasar subset is contaminated with stars misidentified as quasars. Conclusions. Using prior information about quasar proper motions we could provide an independent verification of the parallax zero-point in early solutions based on less than one year of Gaia data.

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Radio astrometry with chromatic AGN core positions

Cited by 66 publications

References 19 publications

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

Revisiting the birth locations of pulsars B1929+10, B2020+28, and B2021+51

Quasars can be used to verify the parallax zero-point of theTycho-GaiaAstrometric Solution

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